Don't just apply for any credit card offer. You have to be patient and wait for the mega promotions. I typically do not apply for a credit card offer of less than 40,000 bonus points/miles. You can find out about mega offers by monitoring just a few specialist blogs which I will list below. Note: Many of these blogs get a commission via the credit card links they offer their deals on. I have no issue with this because for the most part, they deserve it for saving you a lot of time searching for the best deals elsewhere. However, once I know a good offer is available, I always do some more research on the frequent flier forums just to see if the sponsored links the blogs are offering are really are the best deal available.
e.g. I heard about a 30,000 bonus mile promotion for opening a new Delta Airlines American Express card but when I searched the frequent flier forums I found a better bonus offer for 45,000 miles. So you need to find the best offer which is typically a web link posted by fellow travel hackers and apply.
Step #1 - Check these blogs for 40K+ credit card sign-up deals
Frugal Travel Guy
The Points Guy
Million Mile Secrets
Step #2 - Check the forums for potential better promos & offer codes
Step #3 - Apply for a personal and business card at the same time using the 2 browser trick. When you apply for a credit card, the application process often puts a tracking cookie on your computer and won't offer you the same deal twice. Using 2 different browsers gets around this limitation and will typically be only registered as one 'pull' from the credit bureaus.
Step #4 - Bump the bonus. Many credit cards will match the better bonus offered after you apply so long as you email it and request it within 60 days. Chase bumped my 50K Chase Sapphire bonus to 100K they were offering just a few targeted customers simply because I heard about the offer and asked them to.
Check out Ricks FAQ on this topic as you do need to be careful about how often you apply for credit cards.
Check out the rest of my travel hacking tips here.